Reaction vessels of the said type are known and are used in many processes in the chemical industry.
The internally arranged evaporator elements are conventionally constructed in the form of plates, pipe coils, tube bundles or other tubular constructions, a heat transport medium flowing through the plates or tubes which gives off heat via the plates or tube wall to a reaction medium in the reaction vessel or absorbs heat from this. If intensive mixing of the reaction medium is necessary for certain reactions, the convection which the said tubular constructions generate is frequently insufficient and the reaction medium must additionally be mixed by mechanical means, for example via an agitator or via an external circulation pump. An apparatus having such an external circulation is disclosed by EP 0 012 304, in which a process and an apparatus for the continuous preparation of trioxane are described. In this process the trioxane is formed from aqueous formaldehyde in the presence of acid catalysts at elevated temperatures and is separated off from the reaction mixture by distillation. An external forced circulation is responsible for the intensive mixing of the reaction mixture.
A measure of the efficacy of this forced circulation which can be used in this process is the circulation ratio which is defined as the ratio of the amount of liquid circulating, in kg/s, to the amount of liquid evaporated, in kg/s. In the production of trioxane, a circulation ratio greater than 50 is to be sought after, which previously could only be achieved via such an external forced circulation. However, for this, the installation of cost-intensive and high-maintenance apparatuses, pumps and pipes is necessary, which additionally hold safety hazards.
The object of the invention is to improve a reactor of the type mentioned at the outset in such a manner that a sufficient mixing of the reaction medium is possible even without additional mechanical means.